Gary --- I too have a 2003 211(S) and ordered it with G&B tank heaters. The on/off switch is a black rocker switch with a lit red jewel when on. Mine is in between the furnace thermostat and the water pump / water heater switch bank, located on the wall to the left of the "kitchen" sink.
Others --- I continue to get 11-12 MPG driving 65-75 MPH. Dipped to 10.5 on our last trip doing 75-80 into a head wind. Oh well.
Other rigs continue to pique my interest, but in the end they also have similar or other unique "problems". I plan to stay with ours for a few years at least. The devil you know vs the devil you don't know.